This invention relates to integrated circuit fabrication, and, more particularly, to a method and tool to facilitate threading integrated circuit bond wires through capillary tubes in wire bond machines.
Wire bond machines are typically used to attach bond wires between bond pads fabricated on integrated circuit dies and leadframes through which signals and power are routed to and from the integrated circuit. A typical wire bond machine 10 is shown in FIG. 1. The wire bond machine 10 includes a spool 12 of bond wire 14, which is typically gold wire having a diameter of about 1 mil (10xe2x88x923 inches). The wire 14 extends over a diverter 20 and passes through a housing 22 containing a sensor 24 and an air guide 26. The sensor 24 and air guide 26 cooperate with each other in a conventional manner to draw the wire 14 from the spool 12 and maintain the wire 14 at the proper tension. The wire 14 then extends downwardly and passes through a nozzle 30 having a relatively large diameter to a guide tube 34, which also has a relatively large diameter. The guide tube 34 has a flared upper end 36 that facilitates the threading of the wire 14 into the tube 34. The wire 14 then extends through a gap 38, typically 0.5-1.0 inches wide, and passes through a capillary tube. The capillary tube 40 typically has a diameter of about 3.0-3.5 mils. The capillary tube 40 is attached by a clamp 44, to a transducer that produces ultrasonic force.
In operation, it is occasionally necessary to thread the bond wire 14 from the spool 12 to the capillary tube 40 such as, for example, if the supply of wire 14 from the spool 12 has been exhausted or the wire 14 breaks. Threading the wire 14 over the diverter 20 and through the housing 22 is fairly easy. Threading the wire 14 through the nozzle 30 and guide tube 34 is somewhat more difficult, but because of the relatively large diameters of the nozzle 30 and guide tube 34, can generally be accomplished by a skilled operator fairly easily in relatively little time. However, it is substantially more difficult to thread the wire 14 into an end 48 in the capillary tube 40 because of the relatively small diameter of the capillary tube 40. The guide tube 34 is somewhat effective in guiding the wire 14 to the general vicinity of the end 48 of the capillary tube 40, but, because of the gap 34, the wire 14 is easily deflected from the entrance to the capillary tube 40. For example, there may be air currents present that, although slight, are sufficient to deflect the wire 14 away from the end 48 of the capillary tube 40. Even the breath of an operator threading the wire 14 can be sufficient to deflect the wire 14 away from the end 48 of the capillary tube 40. As a result, it is invariably necessary for the operator to manually guide the wire 14 into the end 48 of the capillary tube 40.
The operator typically guides the wire 14 into the end 48 of the capillary tube 40 by grasping the wire 14 with a tweezers (not shown) while viewing the end of the wire 14 through a magnifier (not shown), such as a microscope (not shown). Successfully guiding the wire 14 into the end 48 of the capillary tube 40 in this manner requires a great deal of skill and manual dexterity, and usually requires a great deal of time. During the time the operator is threading the wire 14 through the capillary tube 40, the bond machine 10 may not be used for fabricating integrated circuits. The difficulty in threading the wire 14 through the capillary tube 40 not only results in excessive down-time of the bond machine 10, but may also cause excessive down-time of an integrated circuit fabrication line in which the wire bond machine 10 is used. Further, the skill required to manually thread the wire 14 through the capillary tube 40 reduces the availability of operators capable of operating the wire bond machine 10 and, because manually dexterity and vision may decline with age, may shorten the careers of such operators.
There is therefore a need for a device and method to facilitate the threading of bond wires through capillary tubes, thus reducing the time and skill level required to thread bond wires through a bond machine.
A capillary threading tool is used with a wire bond machine to thread bond wire in though a capillary tube positioned below a guide tube by a gap. The capillary threading tool includes a handle connected to a body portion that is inserted into the gap. The body portion includes a slot through which the bond wire passes between the guide tube and capillary tube. The slot has first and second portions separated from each other along the length of the bond wire. The first portion of the slot has a width that is smaller than the outside diameter of the capillary tube, and the second portion of the slot has a width that is approximately equal to the outside diameter of the capillary tube. The body portion is placed in the gap with the capillary tube inserted into the second portion of the slot beneath the first portion of the slot so that the first portion of the slot substantially fills the gap. The first and second portions of the slot terminate in respective first and second slot ends that are substantially aligned with each other. The capillary tube is placed against the end of the second portion of the slot to align the end of the first portion of the slot with the capillary tube. As a result, the end of the first portion can be used to guide the bond wire into the capillary tube.